1. Field of the Invention
The present invention relates to a light amplifying device, and more particularly to a light amplifying device capable of emitting a light of high energy and hence suitable as a light source for an optical recording device to record information such as characters on a recording medium.
2. Description of the Related Art
Among devices for recording information such as characters on a recording material by the use of a light beam, there is a known laser computer output microfilmer (laser COM), for example, in which a laser beam is scanned in accordance with information output from a computer to directly record the information in the form of characters or the like on a recording material such as a microfilm (see Japanese Patent Laid-Open No. 55(1980)-6772). The laser COM comprises an argon laser for emitting a laser beam, an optical modulator for optically modulating the laser beam in accordance with the information such as characters, a rotatable multifaceted or polygonal mirror for deflecting the laser beam modulated by the optical modulator in a main scan direction, and a galvanometer provided with a deflecting mirror to deflect the reflected light from the rotatable polygonal mirror in a sub-scan direction. With the combination of the rotatable polygonal mirror and the galvanometer, the laser beam output from the optical modulator is two-dimensionally scanned on the recording material through a scan lens, so that the information such as characters is recorded on the recording material.
The above laser COM requires an optical modulator because the former employs an argon laser which cannot be subjected to on/off control. For the reason, it has recently been proposed to use a semiconductor laser in place of the argon laser. However, the power of semiconductor lasers is small in a range from several mW to several tens of mW at most when continuously oscillated. Therefore, semiconductor lasers have difficulties in application thereof to those recording materials which require a laser beam of high energy, e.g., heat mode recording materials such as LDF (laser direct recording films). In addition, OPTICS LETTERS/Vol. 11, No. 5/May 1986, discloses such a technique that laser beams emitted from a plurality of lasers are summed or superimposed coherently by a diffraction grating so as to produce a laser beam in a single polarized state.
The above technique however has several problems as follows. Use of the diffraction grating for summing the plural laser beams makes it difficult to design the grooved surface configuration of the grating necessary for directing all the diffracted laser beams toward a certain direction. Another problem is in that efficiency of the optical system is low because of the need of taking out only the O-order diffraction light through an aperture, while shielding other laser beams diffracted in nonessential directions. Further, a polarized beam splitter is employed to sum the laser beams emitted from two semiconductor lasers. But, the laser beam having been summed contains both a P-polarized light oscillating parallel to the incident plane of the polarized beam splitter and an S-polarized light oscillating perpendicular to that incident plane. Accordingly, if a polarizer is disposed in an optical path lying after summarization into the single beam, 1/2 of the light intensity could not pass through the polarizer.